Lightning arresters in the form of mental oxide varistor discs are used to protect electrical equipment and personnel from overvoltage surges usually caused by lightning. The varistors are arranged within electrically-insulative enclosures singularly or in a stacked array to provide an electrical series circuit whereby the clamping voltage of the arrester is determined by the series addition of the individual varistor clamping voltages.
To provide good electrical connection between the varistors within the stacked array, the varistors are often bound together by polymer filaments prior to insertion within the enclosures and compression springs are positioned at one or both ends to provide compressive forces to the varistors to insure good electrical connection. Spring washers and the like are also positioned between the varistors to provide additional compressive forces for enhanced electrical connection. U.S. Pat. Nos. 4,656,555 and 4,864,456 describe the use of filament windings and compression springs to improve electrical connection between the varistors per se as well as between the varistors and the arrester end terminals. To prevent the build-up of gases during the occurrence of an overvoltage condition, the immediate enclosures are often vented to allow egress of the ionized gases and prevent over-pressure buildup. One example of a lightning arrester having a vented enclosure is found in U.S. Pat. No. 4,930,039.
One purpose of the invention is to provide a double enclosure lightning arrester assembly and handling procedures and strength integrity upon failure condition. Additionally, the double enclosure provides a means of spring loading the varistors to insure good electrical contact. The double enclosure thereby insures good electrical connection between the enclosed varistors as well as providing secure containment of parts within a split cylinder polymer casing. The polymers casing and subassembly is inserted within the main polymer outer enclosure and the entire assembly is bolted together. The resultant lightning arrester exhibits good electrical conduction between the varistors and containment of internal components in case of arrester failure and subsequent fault current conditions.